The present invention relates to a plasma processing apparatus that performs plasma processing, such as film forming or dry etching, on a substrate to be processed.
In recent years, there has been an increasing demand for high-speed plasma processing apparatuses that perform excellent film formation and dry etching at a high speed. Also, there has been a demand for smaller plasma processing apparatuses that require a smaller area, and less initial investment and operation cost.
In a plasma dry etching apparatus, in order to improve the anisotropy of the etching rate and to prevent burning of an organic resist as an etching mask, the heat caused by the plasma irradiation onto the object to be processed is removed by cooling down the stage by means of a refrigerant. In a plasma film forming apparatus, a cooling operation is also necessary if the object to be processed or the thin film has little heat resistance.
Particularly, in semiconductor production, to increase the productivity, the process speed is increased using high-density plasma, and the size of each silicon substrate is enlarged from a diameter of 200 mm to 300 mm so as to increase the number of chips obtained from one substrate. In this manner, the production cost is reduced, and the productivity is increased. However, as the plasma has higher density and the substrate has a larger size, the quantity of heat to be removed per unit time becomes greater. As a result, a larger cooling device is required. When the temperature distribution of the substrate is made uniform, the temperature difference between the inlet and the outlet for the refrigerant needs to be smaller. In such a case, it is necessary to circulate the refrigerant at a very high speed. As a result, a larger circulating device is required. In general, a chiller provided with a cooling mechanism and a circulating mechanism is used.
The stage, on which the object to be processed is placed, comprises an electrostatic chuck mechanism for tightly adhering the object to be processed to the stage, a high-frequency and DC voltage electrode mechanism for generating plasma or controlling the ion irradiation energy from the plasma, a mechanism for filling a gap between the object to be processed and the stage with helium gas so as to improve the heat conductivity between the object to be processed and the stage, and a temperature monitor mechanism for monitoring the temperatures of the object to be processed and the stage.
Conventionally, with the stage to which a DC or high-frequency voltage is applied, an inactive fluoride liquid having a low dielectric constant and low conductivity is used as a refrigerant so as to provide high electrical insulation.
However, the refrigerant used in the prior art has a small specific heat and a low conductivity, and thus is not capable of absorbing much heat. Therefore, the refrigerant is cooled down to xe2x88x9220xc2x0C. or lower by means of a chiller, so that the temperature difference between the refrigerant and the stage becomes greater. With such a refrigerant having a low temperature, heat insulation becomes complicated, because of a long supply pipe for the refrigerant. Furthermore, since such a refrigerant is expensive, a large amount of it makes the entire production cost too high. Therefore, a relatively small refrigerant chiller is normally disposed in the vicinity of a conventional plasma processing apparatus.
An object of the present invention is to provide a plasma processing apparatus that includes a small and inexpensive stage cooling mechanism.
The above object of the present invention is achieved by a plasma processing apparatus that excites plasma in a container and processes an object in the plasma. This plasma processing apparatus includes: a gas supply system that supplies a process gas required for exciting the plasma; an exhaustion system that exhausts the process gas and evacuates the container; and a conductive stage on which the object to be processed is placed, the conductive stage being placed in the container. In this plasma processing apparatus, a DC voltage or high-frequency power is applied to the conductive stage; and a cooling passage for cooling the object to be processed is disposed in the stage. The cooling passage is made of a material having a high heat conductivity so as to transmit heat of the stage to a refrigerant, and a high electrical insulating strength so as not to transmit the DC voltage or high-frequency power applied to the stage to the refrigerant.